1. Field of Invention
The present invention relates to an industrial robot, more specifically relates to an industrial robot having an elevating part elevating and lowering a workpiece.
2. Description of the Related Art
In an industrial robot in which the robot body is driven to be elevated or lowered, when the drive system etc. driving the elevating and lowering operation breaks down, the weight of the robot body itself will sometimes cause the robot body to fall. For example, in an industrial robot transmitting the drive force of a motor by a pulley and a belt hung upon the pulley so as to drive the elevation and lowering operation the robot body, if a power outage etc. occurs during the work, the brake of the motor will maintain the position of the robot body, but if the belt breaks, a part breaks, etc. and power of the motor can no longer be transmitted at all, the robot body will fall.
As a technique for solving such a problem, there is the fall prevention system disclosed in Japanese Patent Publication (Kokai) No. 2002-36164-A. In this fall prevention system, rotation of a drive pulley is transmitted to a driven pulley by a belt. The rotation of the driven pulley is converted to drive force in the vertical direction and used for elevation of the elevation member. The outer circumference of the driven pulley is provided with a stopper for engaging with the driven pulley and stopping the rotation of the driven pulley in accordance with slack or breakage of the belt so as to prevent the elevation member from fall.
In the technique of Japanese Patent Publication (Kokai) No. 2002-36164-A, however, a stopper is engaged with the driven pulley to prevent fall, therefore various inconveniences occur. For example, it is necessary to provide the stopper and a drive mechanism thereof adjacent at the driven pulley, so the degree of freedom in layout is low. Further, if a breakdown has occurred in a portion from the driven pulley to the elevating part, even if the rotation of the driven pulley is stopped, the elevation member cannot be prevented from fall.